Merge pull request #3 from stankud/add-credentials-opt

add credentials option

Author: mlazarov

lib/bunyan-stackdriver.js

@@ -62,6 +62,9 @@ function BunyanStackDriver(options, error) {
   if (options.keyFilename) {
     gopts.keyFilename = options.keyFilename;
   }
+  if (options.credentials) {
+    gopts.credentials = options.credentials;
+  }
 
   var loggingClient = logging(gopts);